Hello, I've had no trouble with my Team Fortress 2 server until last night when my friends were trying to join and they kept saying it wasn't responding, so I looked more in depth to my console and saw this:

received auth challenge; signing into game server account

Then I looked online and people were telling me to go into the game and fix it by typing something in the console and did all that. So now it's saying something like this:

What do you want? The message you see is a message sent by Valve's servers to acknowledge that they have recieved your auth-request for lobbies, quickplay etc. I'd also recommend you to set -ip and -port on your server startup line.